The present disclosure relates generally to toners and toner processes, and more specifically, to toner compositions, in embodiments, possessing excellent charging properties and dispensing performance.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles. In addition, there are illustrated in U.S. Pat. Nos. 5,364,729 and 5,403,693, the disclosures of each of which are hereby incorporated by reference in their entirety, methods of preparing toner particles by blending together latexes with pigment particles. Also relevant are U.S. Pat. Nos. 4,996,127, 4,797,339 and 4,983,488, the disclosures of each of which are hereby incorporated by reference in their entirety.
Toner may also be made by an emulsion aggregation process. Methods of preparing an emulsion aggregation (EA) type toner are known and toners may be formed by aggregating a colorant with a latex polymer formed by batch or semi-continuous emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. In particular, the '943 patent describes a process including: (i) conducting a pre-reaction monomer emulsification which includes emulsification of the polymerization reagents of monomers, chain transfer agent, a disulfonate surfactant or surfactants, and optionally an initiator, wherein the emulsification is accomplished at a low temperature of, for example, from about 5° C. to about 40° C.; (ii) preparing a seed particle latex by aqueous emulsion polymerization of a mixture including (a) part of the monomer emulsion, from about 0.5 to about 50 percent by weight, or from about 3 to about 25 percent by weight, of the monomer emulsion prepared in (i), and (b) a free radical initiator, from about 0.5 to about 100 percent by weight, or from about 3 to about 100 percent by weight, of the total initiator used to prepare the latex polymer at a temperature of from about 35° C. to about 125° C., wherein the reaction of the free radical initiator and monomer produces the seed latex comprised of latex resin wherein the particles are stabilized by surfactants; (iii) heating and feed adding to the formed seed particles the remaining monomer emulsion, from about 50 to about 99.5 percent by weight, or from about 75 to about 97 percent by weight, of the monomer emulsion prepared in (ii), and optionally a free radical initiator, from about 0 to about 99.5 percent by weight, or from about 0 to about 97 percent by weight, of the total initiator used to prepare the latex polymer at a temperature from about 35° C. to about 125° C.; and (iv) retaining the above contents in the reactor at a temperature of from about 35° C. to about 125° C. for an effective time period to form the latex polymer, for example from about 0.5 to about 8 hours, or from about 1.5 to about 6 hours, followed by cooling. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Toner systems normally fall into two classes: two component systems, in which the developer material includes magnetic carrier granules having toner particles adhering triboelectrically thereto; and single component systems, which generally use only toner. Of the one-component development systems, both magnetic and non-magnetic systems are known. Magnetic systems involve the use of a toner containing a magnetic substance, which may preclude the development of sharp color images, which has led to a focus on non-magnetic systems.
The operating latitude of a powder xerographic development system may be determined to a great degree by the ease with which toner particles may be supplied to an electrostatic image. Placing charge on the particles, to enable movement and development of images via electric fields, is often accomplished with triboelectricity. Triboelectric charging may occur either by mixing the toner with larger carrier beads in a two component development system, or by rubbing the toner between a blade and donor roll in a single component system. However, non-magnetic single component development (SCD) toner requires high flowability and high chargeability, sometimes greater than that required for conventional two component development (TCD) toner.
With non-magnetic SCD, toner is supplied from a toner house to the supply roll and then to the development roll. The toner is charged while it passes a charging/metering blade. Non-magnetic SCD has been very popular for desk top color laser printers due to its compact size since it does not need carrier in the development housing to charge toner. Non-magnetic SCD systems may thus utilize cartridges that are smaller in size compared with TCD systems, and the cost to a customer to replace a unit may, in some cases, be lower for a single component development system compared with a two component system. The development area may require toner with high flowability to move to the photoreceptor. The toner should be robust throughout the life of the Customer Replaceable Unit (CRU) for the toner, which is typically about several thousand pages to a couple of tens of thousands of pages.
There are several problems with SCD. The first is low charge and broad charge distribution on toner particles compared with conventional TCD toner. This is because the time for toner to flow through the gap between the blade and the development roll is very short. Low charge causes high background and low developability. Toner for SCD also has a high fines content. The fines content in toner also affect the charge and the print background. The higher the fines content, the broader the charge distribution.
Another problem with SCD includes toner robustness in aging and in extreme environments such as A and C zone conditions. The high stress under the blade may cause the toner to stick to the blade or the development roll. This may reduce the toner charge and the toner flowability. Since non-magnetic toner is charged through a charging/metering blade, low charging and low flowability can cause print defects such as ghosting, white bands, and low toner density on images.
Hence, it would be advantageous to provide a toner composition with excellent charging characteristics and excellent dispensing performance.